1. Field of the Invention
The present invention relates to an operation microscope having a moveable main body unit of the microscope to permit movement of the observation (viewing) field or to change the observation direction.
2. Description of Related Art
In general, operation microscopes are used to observe the affected part in an enlarged manner during medical operations. Also, operation microscopes may function as eyes of operators during operations, and thus are desirably allow the observation fields or observation directions of the operation microscopes to be moved or changed like human eyes. In particular, moving of observation fields and changing of observation directions of these operation microscopes are frequently performed in brain neurosurgical operations.
In general-purpose microscopes used in the brain neurosurgical operations, gravity moments are canceled with each other, and positioning of the observation fields and the observation directions are manually performed. In other words, operators must take their hands off from the affected part every time the observation fields are moved and the observation directions are changed. As a result, the operation time would be prolonged, resulting in overload for not only the operators, but also the patients. To relieve this problem, a mechanism for automatically moving the observation fields and for automatically changing the observation direction is used.
In this case, the mechanism for automatically moving the observation field corresponds to a mechanism for moving an observation field in a fine mode. By this mechanism, moving of the observation field can be performed by using a foot switch without removing a hand of an operator from the affected part. Also, in this observation field moving mechanism, actuators are provided with respect to two mutually perpendicular rotation axes. A main microscope body can be swung by the actuators around the rotation axes. Thus, the focal point of the main microscope body is moved on a spherical surface where the cross point of the rotation axes is at the center of rotation. As a consequence, the observation field can be moved.
In a similar manner, the observation direction can be changed without removing the hand of the operator from the affected part. In this observation direction changing mechanism, the observation direction is changed by swinging the main microscope body, with the focal point of the main microscope body at the center of rotation.
While the medical operation is carried out by using the operation microscope, the focusing is frequently achieved by moving of the main microscope body. For example, as shown in FIG. 14, focusing is carried out by moving the main microscope body 70 along the direction of the observation axis OZ. In this case, the distances between the focal point P of the main microscope body 70 and the moving rotation axes OX and OY are different before and after the main microscope body 70 is moved. As a consequence, even if the rotational velocity (angular velocity) of the main microscope body 70 is constant, the velocity of the focal point P is changed, so that the apparent velocity of the observation field is changed.
Also, when the observation magnification of the observation field is changed from low magnification to high magnification, the observation field appears to be closer to the operator. Thus, the apparent velocity of the observation field is different at different magnifications even if the actual velocity of the focal point P is constant.
Moreover, when the main microscope body unit 70 is rotated about rotation axis OY, perpendicular to the observation axis OZ, so as to move the focal point P, the distance between the focal point P and the moving rotation axis OX perpendicular to the rotation axis OY is changed. As a consequence, after the focal point P is moved by rotation about rotation axis OY perpendicular to the observation axis OZ, if the main microscope body 70 is thereafter rotated, the apparent velocity of the observation field in the case wherein the body 70 is rotated about rotation axis OY is different from that of the observation field in the case wherein the body 70 is rotated about rotation axis OX.
As to the changing velocity of the observation direction, a similar phenomenon to that for the apparent velocity of the observation field will occur.
As described above, the conventional operation microscope has the following problems. When the observation conditions such as the focal position, the focal distance, the observation magnification and the like are changed and the observation states such as the inclination of the main microscope body are changed, either the apparent velocity of the movement of the observation field or the apparent velocity of the change in observation direction depends on before and after these conditions and states are changed. Thus, to maintain a consistent display, the operator must readjust the actual velocity of the main microscope body every time the observation condition or state is changed. This may interfere with a medical operation which needs great urgency.